a) Field of the Invention
The present invention relates to communications systems in general and in particular to resource reservations within said communications systems.
b) Prior Art
A conventional communications system or network is comprised of a plurality of nodes coupled by an interconnect medium. Communication is effected by one node termed “Source Node” sending data to another node termed the “Destination Node”. In order to maintain a particular Qualify of Service (QoS) the Destination Node must reserve sufficient resources to process the data without undue delay. In fact, not only must the destination node reserve sufficient resources but any intermediate node that the data must traverse before reaching its destination must also reserve sufficient resources to ensure prompt processing of the data within these intermediate nodes. For example, the nodes must have enough storage space to buffer the data before processing. If adequate buffering is not available the node may have to discard the data. In this example storage is a resource. But, in general, a resource can be anything required to receive and process data. As a consequence a resource may include memory space, processor cycle, link, bandwidth etc.
The prior art provides several flow control proposals for managing data flow within communications networks. Resource management is an integral part of the flow control method. The prior art flow control proposals include Braden et al; Resource Reservation Protocol (RSVP), IETF RFC 2205, September 1997. The RSVP provides for receiver-initiated setup of resource reservation. In other words the destination node reserves resources based on a message sent by a source node. The RSVP protocol can be used by a host to request bandwidth from the network for data flows. The RSVP is usually used by routers to deliver bandwidth requests to all nodes along the patch or paths of a flow. The node issuing the RSVP can also request confirmation assuring that the request has been installed in the network. One of the drawbacks is that the RSVP protocol reserves resources only for simplex flows. Stated another way, RSVP requests resources in only one direction. To this end RSVP treats a sender (source) as logically distinct from a receiver (destination) even though the same application process may act simultaneously as both a sender and receiver.
In another flow control scheme termed “Rate Base” the rate at which data is permitted to be delivered from a source to a destination is controlled via a feedback signal from destination to source. If resources are available at the destination the source may transmit data without restriction. If resources at the destination are in short supply or unavailable the rate of transmission is restricted to the point of cut off altogether. One such rate base technique is described in an ATM document #94-0735 entitled “Enhanced Proportional Rate Control Algorithm” by Larry Roberts, August 1994.
In yet another flow control scheme termed “Credit Base Control”, a destination node generates and forwards “credits” to the Source node which may only transfer data if it has credits outstanding. The credits reflect the ability of the destination node to handle data. One such credit base controlled system is described in an ATM Forum document #94-0632 entitled “Credit-Based Proposal for ATM Traffic Management by Hunt et al., July 1994.
Because the above techniques treat the Source Node and Destination Node as separate entity when in fact they may not, a more dynamic system and method for managing data flow including Resource Reservation is required.